In recent years, with the growing trend toward digital broadcasting, digital television and radio broadcasting services have been launched throughout the world.
Especially in Europe, DVB-T (Digital Video Broadcasting-Terrestrial) and DAB (Digital Audio Broadcasting) services of transmitting a plurality of programs by time-division multiplexing are already available. In addition, mobile reception of the broadcast with PDAs (Personal Digital Assistances) is under development.
Turning now to the field of communications, more and more AV (Audio Visual) devices are equipped with Bluetooth and wireless LAN (Local Area Network) capabilities, and wireless communication services, such as mobile phones and wireless access to the Internet, have reached the stage of practical use.
In view of the circumstances, AV devices, mobile phones, PDAs each applicable to both broadcast reception and wireless communications have been suggested aiming to offer convenience to users.
As one example of such a device, JP patent application publication No. 11-112379 discloses a wireless communication device having a double function of a radio broadcast receiver and a radio telephone.
FIG. 8 is a functional block diagram showing a main part of the above wireless communication device. When the wireless communication device acts as a radio telephone, a communication signal received with an antenna 901 is converted to an audio signal through the processing conducted by an RF (Radio Frequency) unit 902 for radio telephone system, a TDMA (Time Division Multiple Access) unit 903, and an audio CODEC (COder and DECoder) 904. The audio signal is outputted as sound from a speaker 905. Also, an audio signal picked up by a microphone 909 and selected by a switch 910 is converted to a communication signal through the processing conducted by the audio CODEC 904, the TDMA unit 903, and the RF unit 902. The communication signal is transmitted from the antenna 901.
On the other hand, when the wireless communication device acts as a radio broadcast receiver, a broadcast signal received with an antenna 907 is converted to an audio signal by a radio broadcast receiver 908, and passed sequentially to the switch 910, the audio CODEC 904, and the speaker 905 where the audio signal is outputted as sound.
The above wireless communication device, however, has problems as follows. To receive a communication signal and a broadcast signal which are of different frequencies, the wireless communication device performs frequency conversion using two different local signals that are separately generated by the RF unit 902 and the radio broadcast receiver 908. With this structure, the two local signals interfere with each other, and the interference impairs the noise margin, operational stability, and adjustability of the device.
Further, there is another problem. Provision of two sets of a local oscillator and a frequency converter for generating respective local signals makes it difficult to reduce the device size.
The problems noted herein are inevitable if the above structure is applied as it is to a wireless communication device for handling, for example, the DVB-T service and radio communication service.